Biaxially oriented polypropylene (BOPP) films used for packaging, decorative, and label applications often perform multiple functions. It must perform in a lamination to provide printability, transparent or matte appearance, or slip properties; it sometimes must provide a surface suitable for receiving organic or inorganic coatings for gas and moisture barrier properties; it sometimes must provide a heat sealable layer for bag forming and sealing, or a layer that is suitable for receiving an adhesive either by coating or laminating.
Matte appearance can be achieved by addition of organic or inorganic particles, but these processes usually affect the clarity and transparency of the BOPP films and also add cost to the manufacturing process, and are not suitable for certain packaging applications for aesthetic reasons for they negatively impact the visual appeal of the printed job. Another way to obtain matte appearance in BOPP films is to coat the surface layer, but this option is also usually undesirable because these coatings are expensive and also negatively impact the visual appeal of the printed job, and in order to be effective they need to be used at a level that imparts significant cost to the BOPP film. All these processes also increase the coefficient of friction of the matte surface of the film, which is undesirable because it can limit the operational speed of the converting processes, which in turn decreases productivity.
In addition, most matte appearance BOPP films in the current marketplace exhibit not only low gloss, but also very high haze. While the low gloss is desirable for the aesthetic appearance of a matte-looking package, the high haze can cause a loss of graphic clarity or “pop.” The high haze of conventional BOPP matte films can mute or “wash-out” or lessen the color saturation of many printing inks used for the packaging graphics. Often, the color palette or color choices can be limited by the use of conventional matte films due to this loss of color saturation.
U.S. Pat. No. 8,431,234 B2 describes a heat sealable matte film formulation using a matte resin formulation of 15-30 wt % metallocene-catalyzed butene-propylene elastomer and 85-70 wt % of a matte resin including ethylene homopolymer and propylene homopolymer or copolymer. However, the film has a high haze >60%.
U.S. Pat. No. 5,474,820 A describes several multilayer polypropylene matte film formulations of polypropylene homopolymer and copolymers, ethylene, propylene, butylenes and other α-olefin having 5 to 10 carbon atoms and HDPE. However, the film has a high haze >30%.
EP Patent 0538746 B1 describes a matte film formulation using a matte resin formulation of 20-80 wt % HDPE and propylene homopolymer. However, the film has a high haze of >40%.
There remains a need in the art for new and improved methods for making matte films with new and improved optical properties. The inventors have found a solution that balances the attributes of matte appearance and low haze by adding an amount from 1-90 wt % of high density polyethylene (HDPE), medium density polyethylene (MDPE), low density polyethylene (LDPE) or linear low density polyethylene (LLDPE) to polypropylene (PP).